The present invention relates to ignition systems for internal combustion engines and particularly to an ignition system for optimizing the ignition timing of a four-cycle internal combustion engine.
It has been discovered that in a multi-cylinder four-cycle internal combustion engine the octane requirement of a few cylinders; for example, one or two, will greatly exceed the octane requirement of the remaining cylinders. The term `octane requirement` refers to the octane number of the fuel required to obtain substantially knock-free performance from an engine or a particular cylinder at the designed ignition timing. The term `knock` refers to the condition where a fuel auto-ignites in the cylinder causing severe pounding or knocking. It is the present practice to adjust the ignition timing of the engine so that the engine has no audible knock when operating on a particular gasoline. With this adjustment, the majority of the cylinders are operating with a retarded ignition timing while one or two are operating at or near the optimum timing.
At the present state in development of internal combustion engines, particularly those for use in automobiles and light duty vehicles, emission standards require the use of a catalytic converter. The use of a catalytic converter requires the use of unleaded gasoline. It is extremely expensive to increase the octane rating of unleaded gasoline since any increase requires quality high octane components that are only available from sophisticated refining operations. Thus, it has been the practice to retard the ignition timing on modern automobile engines operating on unleaded gasoline to eliminate, or at least reduce, their tendency to auto-ignite or knock. Normally, a clean engine will operate on available regular unleaded gasoline at near its designed ignition timing but as deposits build up in the cylinder heads with use, the tendency to pre-ignite or knock increases. As explained above, the auto-ignition or knocking of the engine usually occurs in only one or two cylinders in a multi-cylinder engine. For example, in a 1977 8-cylinder automotive engine, the clean engine octane requirement was approximately 84 octane. After the deposit buildup had reached equilibrium, six of the cylinders required approximately 90 octane while one cylinder required 93 octane and one cylinder required 95 octane. If an attempt was made to run this engine without knock, the ignition timing would have to be severely retarded to prevent the cylinder that required a 95 octane gasoline from knocking. This amount of ignition timing retardation would severely affect the efficiency of the remaining six cylinders which required only a 90 octane gasoline. The loss in efficiency would affect the overall economy of the engine as well as its performance.